There are generally two varieties of sleeping bags. One type is a rectangular, zippered bag having top and bottom panels. A second type is a so-called mummy bag having a substantially single-piece casing that can be opened at least along the upper head portion of the bag. Both types of bags are filled with an insulating thermal material such as down. A problem associated with both types of sleeping bags is that when they become soiled, they are very difficult to wash. Furthermore, repeated washing of sleeping bags usually produces an uneven mat of the thermal material, leading to a loss of insulation value of the bag.
Sleeping bag liners have been used in the past to prevent sleeping bags from becoming soiled. The liners were removable and could be washed. One such liner was completely nonattachable to a sleeping bag. Another such liner was attachable by tying strings on the sleeping bag to loops on the liner. Problems which have occurred with these previous liners include the foot portion of the liner becoming entangled with the feet of the user, and the head portion of the liner sliding downward into the bag, leaving the upper edge opening of the sleeping bag, the part which wraps around a user's neck or head, unprotected.